1. Technical Field
The inventive concept relates to a semiconductor memory apparatus and, more particularly, to a phase change memory apparatus and a method of manufacturing the same.
2. Related Art
A phase change random access memory (PCRAM) device is regarded as a non-volatile memory device and has a fast operation speed and a high integration.
The phase change memory device includes a switching device to select a memory cell. Currently, a diode is used for the switching device of the PCRAM device. The diode is formed by forming an insulating layer having a hole type pattern on an active region of a semiconductor substrate, forming a selective epitaxial growth (SEG) layer within the hole type pattern of the insulating layer through a SEG process, and implanting ions into the SEG layer.
As shrinkage of the device increases, it lacks a margin for the hole type patterns such that it can not form the hole type patterns at a desired size and it is difficult to form the hole type patterns having a uniform size in each of the cell strings. In addition, as a diameter of the hole type pattern decreases, the SEG layer is abnormally grown. The fabrication error causes an amount of diode current flowing through each of the phase change memory cells to vary, thereby deteriorating operational reliability of the device.
Meanwhile, as the PCRAM device is more highly integrated, a word line resistance increases. Accordingly, metal contacts are formed between the cell strings and a metal word line is formed to be connected to the metal contacts. In this case, it can solve the problem of the increase in the word line resistance, but the word line metal contacts should be formed for every unit cell string such that the problem of the increase in the chip size still remains.
In addition, the active region to which the word line metal contacts are connected thereto has a relatively higher resistance as compared with a metal word line. Accordingly, the resistance becomes different relative to the spaced distance between the word line metal contact and the unit cell such that the current driving capacity of the diode becomes different depending on the arrangement position of the selected cell. This results in degradation of the operation uniformity, as the number of unit cells constituting the cell string increases. Therefore, it limits the number of unit cells contained in the cell string such that a large number of word line metal contacts are necessary.